In the co-pending, commonly assigned application of Bosche et al, Ser. No. 412,963, filed Nov. 5, 1973, now U.S. Pat. No. 3,987,484, there is disclosed an improved programmed display system, particularly adaptable for educational and instructive purposes, wherein a generally available dynamic storage medium, such as video magnetic tape, is employed. The tape includes the usual audio and video information tracks, in the form of a longitudinal audio track for aural presentation, a longitudinal video control track and diagonal video tracks, as well as a program track which extends the length of the tape, parallel to the audio track used for the aural information. Such tapes and appropriate playback systems are available on a commercial basis.
The program track is provided with messages to indicate the position of the tape and to enable the tape to be advanced or returned to predetermined positions for branching on a selected basis in response to operator inputs to questions or situations presented to him by the aural or visual information. After a branching operation has been completed and in response to the operator activating a numerical input or clear control, the tape is automatically indexed to a designated location in the presentation medium.
The operator has the ability to index the tape to any desired location, in accordance with a directory with which he is provided, or to provide a temporary stop (pause) in the presentation of the material. The operator also may cause the tape to repeat segments of the most recently presented material relating to a particular subject, or to skip designated portions of the presented material.
To achieve the skip, repeat, indexing and branching operations and to reach the designated location in a minimum of time, the tape is selectively driven in the forward or reverse directions at speeds considerably in excess of the normal forward (play) speed and automatically pauses upon arrival at those locations. Also, the tape can be driven, at will, at high speed in either direction in response to commands from the operator.
Because the tape can be driven at widely varying speeds, over at least a 10:1 speed ratio, the detection of tape location information from the program track presents certain problems, relating, for example, to the variable frequency of the program track signals, tape jitter (f.m.), and frequency response of pick-up heads and playback circuits. In addition, to enable the system to be utilized with commercially available systems, only one program track can be employed.